The present invention relates to communication systems, memory systems, and integrated circuit (IC) devices.
Over the last few decades, the use of communication networks has exploded. In the early days of the Internet, popular applications were limited to emails, bulletin board, and mostly informational and text-based web page surfing, and the amount of data transferred was usually relatively small. Today, Internet and mobile applications demand a huge amount of bandwidth for transferring photo, video, music, and other multimedia files. For example, a social network like Facebook processes more than 500 TB of data daily. With such high demands on data and data transfer, existing data communication systems need to be improved to address these needs.
CMOS technology is commonly used to design communication and memory systems. As CMOS technology is scaled down to make circuits and systems run at higher speed and occupy smaller chip (die) area, the operating supply voltage is reduced for lower power. An important factor in device operations is slew rate, which is a ratio of a rise or fall in voltage to the amount of time that rise or fall takes. Consequently, slew rate is a quantity which can be a controlling factor in the performance characteristics of a device. A device having a low slew rate can degrade the performance and speed of a system containing the device, while a device having a high slew rate may not allow the system to react to changes in the state of the device, and thereby cause breakdown of the system. These limitations provide significant challenges to the continued improvement of communication systems scaling and performance.
Process variations between different fabrication processes can cause large variations it device characteristics, such as drain to source current. Such variations in device characteristics make it difficult, if not impossible, to insure that a device will exhibit slew rate characteristics within the performance window as set forth by a manufacturer. Accordingly, improvements to slew rate control in integrated circuit devices are highly desirable.